Poliomyelitis is a neurological disease characterized by paralysis of the extremities and occasionally other muscles, leading to transient or permanent impairment, and rarely, in the most severe bulbar cases, death. Interest in poliomyelitis and poliovirus increased dramatically at the beginning of the 20th century because a relatively rare sporadic illness changed to an epidemic disease with a clear trend to global spread. Due to the very low paralysis-to-infection ratio, some limited circulation of wild poliovirus (WPV) without overt clinical manifestations cannot be fully excluded as the explanation for orphan isolates. Since the early days of oral poliovirus vaccine (OPV), it has been known that the use of this vaccine can cause vaccine associated paralytic poliomyelitis (VAPP) among vaccine recipients and their immediate contacts. Another category of vaccine-derived poliovirus (VDPV), called immunodeficiency-associated VDPVs (iVDPVs), have been isolated from immunodeficient patients chronically infected with poliovirus. The most serious challenge, however, is to greatly strengthen routine immunization within the Expanded Program on Immunization (EPI), which is clearly inadequate in many low-income countries. The successful reintegration of polio eradication activities into the EPI, by also helping to reinvigorate the EPI, can be one of the enduring legacies of the Global Polio Eradication Initiative (GPEI) and serve as a model for other global infectious disease control and eradication initiatives.

Radial neighbor-joining trees of VP1 sequence relationships of representatives of WPV genotypes detected since the launch of polio eradication activities in the Americas in 1985. Genotypes believed to be extinct and surviving genotypes are shown by dashed and solid lines, respectively. Sequences representing the extinct genotypes usually are from the last known isolate of that genotype. (Source: WHO GPLN.)

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Figure 2.

Radial neighbor-joining trees of VP1 sequence relationships of representatives of WPV genotypes detected since the launch of polio eradication activities in the Americas in 1985. Genotypes believed to be extinct and surviving genotypes are shown by dashed and solid lines, respectively. Sequences representing the extinct genotypes usually are from the last known isolate of that genotype. (Source: WHO GPLN.)

Progressive eradication of WPV genotypes, 1986 to 2009. Countries that have never eradicated indigenous WPV circulation are shown in black; reinfected countries are represented in dark grey. Numbers indicate the location and year of the last detection of an indigenous WPV genotype. (Source: WHO GPLN.)

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Figure 3.

Progressive eradication of WPV genotypes, 1986 to 2009. Countries that have never eradicated indigenous WPV circulation are shown in black; reinfected countries are represented in dark grey. Numbers indicate the location and year of the last detection of an indigenous WPV genotype. (Source: WHO GPLN.)